Given that the income was reported on a 1099R, it's a virtual certainty that the IRS will notify the OP. But that notice will take roughly a year to arrive. In the mean time, interest and penalties for late payment are accruing.

Both of which can be avoided by amending the return before April 17. Or - if you want to really get into esoterica - the OP can paper file a new 1040 (not a 1040X) by April 17 and write "superseding return" in red letters across the top. Again, any payment not already made will need to be included with the return. I've only done this once in my career, so it's not very common. I prefer the 1040X, since the people who open the mail at the IRS will know what to do with a 1040X.

Announcements

Disclaimer:
In accordance with IRS Circular 230, you cannot use the contents of any post on The Motley Fool's message boards to avoid tax-related penalties under the Internal Revenue Code or applicable state or local tax law provisions.

When Life Gives You Lemons
We all have had hardships and made poor decisions. The important thing is how we respond and grow. Read the story of a Fool who started from nothing, and looks to gain everything.

Work for Fools?
Winner of the Washingtonian great places to work, and Glassdoor #1 Company to Work For 2015! Have access to all of TMF's online and email products for FREE, and be paid for your contributions to TMF! Click the link and start your Fool career.